1. Plate 14
Staining Bacteria

2. Why Stain?
Most cells lack color, so you must stain them in order to see them

3. Charges Positive molecules attract ________ molecules negative
Positive molecules repel ________ molecules
Negative molecules attract ________ molecules
Negative molecules repel ________ molecules
negative
positive
positive
negative

4. Staining
Positively charged dye molecules are attracted to the negatively charged cytoplasm
Negatively charged dye molecules are repelled by the negatively charged cytoplasm

5. Simple Staining Only one color used
Crystal violet dye is positively charged, which is attracted by bacteria cytoplasm

6. Negative Staining A negatively charged dye is used
What effect will this have on the bacteria cytoplasm?
The cytoplasm will repel the dye
The background will be stained, but not the bacteria cell
Looks like the night sky

7. Heat Fixing Cells need to be adhered to the slide using heat
Like an egg frying on a pan
As proteins are heated, they denature and stick to the surface
We will heat the slides for 2-3 minutes on a hot plate

8. Gram Staining
Gram staining involves a series of staining steps used to differentiate between 2 types of bacteria cells
Gram positive cells – stain blue
Gram negative cells – stain red

9. Gram Staining Steps Add crystal violet dye (wait 1 minute)
Wash slide with water
Add Gram’s iodine to lock in stain (wait 1 minute)
Add alcohol decolorizer to remove stain from Gram negative cells
Add safranin dye (wait 1 minute)

10. Warm-Up What is the purpose of staining cells? How do stains work?
What is the purpose of Gram staining?
What 2 dyes are used in Gram staining?
What are the steps of Gram staining?

13. Bacterial Cells Ideal age for Gram staining bacteria cells is 24 hours
Gram positive bacteria are susceptible to certain antibiotics (like penicillin)
Gram negative bacteria are susceptible to other types of antibiotics